1. Field of the Invention
The invention relates to polymeric foam tube for pipe insulations, wherein the tube has an external surface and internal surface the latter being provided with an adhesively bonded additional layer.
2. Description of the Background Art
The invention further relates to a method for continuously producing a polymeric foam tube for pipe insulations, wherein the polymeric foam tube is extruded providing an external and an internal surface, the extruded tube is axially slit from its external surface to its internal surface, the slit tube is spread to the shape of a plate, an adhesive layer is applied to the exposed internal surface of the tube spread to the shape of a plate, an additional layer is applied to the adhesive layer and bonded thereto, and the spread tube is returned into its tube shape before being slit with closing the axial slit of the tube coated with the adhesive layer and the additional layer.
Such a polymeric foam tube and method for its continuous production is disclosed in EP 1 208 962 A1. The additional layer consists of a material acting as a sliding layer, if a pipe is inserted into the insulation tube. The additional layer can be re-enforced by fibers or can consist of a foamed sheet material, for example polypropylene.
According to the above-mentioned steps of production, the tube with the additional layer on its internal surface has in its final state an optimal connection of the slit faces, which faces are connected by welding or bonding, wherein the tube has the same original shape as when the faces where slit or cut.
Polymeric insulation foams may be produced in numerous ways, of which foam extrusion is one of the most widely used, and known, technologies. Foaming in an extrusion may be the result of either a physical or a chemical blowing process. In the physical blowing process, a volatile gas is mixed with a polymer, and the mixture expands rapidly as it exits the extruder to the ambient pressure. In the chemical blowing process, the volatile gas is formed by chemical reaction, which may be a result of degradation of an additive, or directly caused by the polymerisation reaction.
One of the drawbacks of polymeric foams is the thermal resistance of it. Typically all foams collapse close to the melting point of the matrix polymer, and therefore they are very limited in terms of service temperature. In pipe insulation, the critical point is the contact to the pipe, and if this contact could be diminished, an improved thermal resistance would be obtained. In such a case it is necessary that the layer that is used to insulate the pipe from the foam has a high thermal resistance and a low thermal conductivity. By definition high thermal resistance is needed, and here a selection of layer material plays an important role. A low thermal conductivity on the other hand is not an easy task, since the thermal conductivities of typical materials are much higher than desired.
Also, in the case of certain foam-pipe combinations, for example polypropylene and copper (Cu), degradation of the foam may be observed due to chemical reaction at the interface.
DE 196 35 214 A1 discloses a multi-layered sheet insulating material for heat insulation and sound proofing. The material has at least two separation layers made of a flexible material, such as sheets, non-woven fabric, paper or the like, and spacer elements between the separation layers. The spacer elements are formed by spacer fibers which are oriented perpendicular to the separation layers. The one ends of the spacer fibers are adhesively bonded to a separation layer in bunches of parallel fibers, which bunches are arranged in a distance to each other and according to a prescribed pattern. The other ends of the spacer fibers contact the other separation layer which rests on the other fiber ends. The function of the fibers is to maintain the distance between the two separation layers under the condition to keep heat conduction between the two separation layers as near as possible to that of the included air.